1. Field of the Invention
The present invention relates to a radiation image capturing apparatus that includes a radiation detector for detecting a radiation image of a subject and generating electrical signals representing the detected radiation image. More particularly, the present invention concerns a radiation image capturing apparatus that includes a mechanism for cooling the radiation detector.
2. Description of the Related Art
In a radiation image capturing apparatus, such as an X-ray breast image capturing apparatus (e.g., a mammography apparatus) or the like, a radiation image is generated by exposing a subject (patient) to radiation and recording the radiation in a radiation image recording unit (i.e., a radiation detector). The radiation image recording unit is thereafter scanned with reading light emitted from a reading light source, which is moved relative to the radiation image recording unit, in order to read out therefrom the information associated with the recorded radiation image. An example of such a radiation image capturing apparatus is disclosed in U.S. Pat. No. 6,268,614, which is incorporated herein by reference in its entirety.
Examples of a radiation image recording unit, which can be used in the above-mentioned apparatus, include a radiation detector having a plurality of photoelectric conversion elements and thin-film transistors (TFT), or a light readout type, a light conversion type, or a direct conversion type of radiation detector.
In such a radiation image capturing apparatus, it is necessary to maintain a proper temperature range because of constraints on the temperature characteristics of the photoelectric conversion elements, the effects of thermal noise generated by the electrical circuit, and the like. Therefore, a radiation image capturing apparatus is provided with an air or water type of cooler therein. One example of such an apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2000-037374, which is incorporated herein by reference in its entirety.
The radiation image capturing apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-037374 is directed to effective cooling of the radiation detector. As can be seen in FIG. 1 of the above-mentioned publication, the radiation image capturing apparatus includes a two-dimensional radiation detector 5 and a signal converter 6, which are contained in the housing 4 of an image capturing unit 3 in this order from the front of the housing 4. The housing 4 is provided with a fan 7, which acts as a cooling means, on an upper portion thereof. A lower portion of the housing 4 is provided with an inlet port 4a for introducing outside air. Release of heat generated by the two-dimensional radiation detector 5 is accomplished by actuating the fan 7, and thereby introducing air into the housing 4 through the inlet port 4a. 
In the apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-037374, the inlet port 4a is formed at one end of the radiation detector 5, while the fan 7 is located at the other end of the radiation detector 5 so that cooling of the whole radiation detector 5 can be achieved. In many radiation image capturing apparatuses, however, the arrangement of the radiation detector within the image capturing unit is restricted for various reasons. If the image capturing unit is a mammography apparatus, for example, the image capturing unit is required to be movable around the breast, so that image capturing of the breast from different directions can be performed. Consequently, a large size for the image capturing unit housing is not permitted, and the radiation detector must be contained within a small space. Furthermore, since image capturing up to the base of the breast is required, the radiation detector must be located within the housing such that the distance between the radiation detector and the chest wall of the patient becomes suitably short during a mammography examination. Thus, the radiation detector is located on the chest-wall side of the housing, forming a narrow space between the radiation detector and the portion of the housing nearest to the chest wall of the subject. Such an arrangement causes insufficient heat to be released from the radiation detector. This results in non-uniform cooling of the radiation detector, which in turn tends to reduce imaging accuracy.